Anãs Brancas Pulsantes

S.O. Kepler

IF/UFRGS

As 98% of all stars evolve into white dwarf stars, their study tell us about the evolution of the majority of stars. White dwarf stars show luminosity variations when their temperature reach instabilitity strips caused by high surface opacity. These variations are due to global pulsations that can be used to study the internal structure and evolution of the stars. Their observations can be used as laboratories to test physical theories at high density and temperature. We have been using extensive data sets of time series photometry acquired over the last three decades to measure the rate of change of the pulsation periods of white dwarf stars, which in turn measure their evolutionary rates. The evolution of an isolated white dwarf is dominated by cooling. However, hot pre white dwarfs also show significant radius evolutionary rates. After 30 years of observations we finally measured the cooling rate of a DAV, G117-B15A, in good agreement with the theoretical predictions. We also measured the faster evolutionary rate in the DOV PG 1159-035, as well its mass with unprecedent precision.